Fuse construction



April 7, 1970 P. E. MERTRYILVL ET-AL 3,505,630 7 FUSE CONSTRUCTION Filed Jan. 29, 1968 FIG-4,84

INVENTORS PHILLIP EDWARD MERRILL EMIL ROBERT PLASKO THEIR ATTORNEYS United States Patent U.S. Cl. 337-201 12 Claims ABSTRACT OF THE DISCLOSURE An electric current sensitive fuse is disclosed including an electrically insulative rod or cylinder with a current carrying length of fuse wire extending along a surface of such rod. Two spaced conductive current terminal fuse wire holders are carried by such rod and are connected at each end of such length of fuse wire. Electric current passing through such length of fuse wire below the ampere rating of the fuse flows through the fuse wire while causing said rod surface to dampen vibrations in such length of fuse wire. Electric current above the selected ampere rating of the fuse causes such length of fuse wire to blow.

This invention relates to a fuse construction.

In conventional fuses of prior construction, the fuse wire is suspended between the centers of two metal end caps.

We have discovered that a disadvantage of this construction includes the fact that there is no dampening of vibration of the fuse wire, thereby making such wire' susceptible of being broken under severe vibration conditions. We have discovered that this vibration problem is quite severe. We have also discovered that since most fuse wires expand as they are heated by the electric current, such expansion makes them somewhat loose, which in turn permits severe oscillation, which in turn causes breakage of the fuse wires.

Other prior fuses use prestressed wire, such as coiled wire, extending between the metal caps of the fuse. We have discovered that while such construction keeps a slight tension on the wire, the extra mass and length involved do not eliminate the vibration problem.

According to our invention, a construction is provided whereby the foregoing objectionable vibrations are prevented and damped in a manner which becomes apparent as the description proceeds with reference to the accompanying drawings in which:

FIGURE 1 is a side view of a fuse according to this invention drawn to scale in the application patent drawings, and an electric current system connected therewith.

FIGURE 2 is an enlarged cross section of the fuse shown in FIGURE 1.

FIGURES 3, 4, 5 and 6 are cross sections of other embodiments of this invention.

FIGURE 7 is an enlarged cross section of a portion of FIGURE 6 taken along the plane 77 of FIGURE 6.

Certain words may be used in this specification and in the accompanying claimed subject matter which indicate direction, relative position, and the like. Such words are used for the sake of clearness and brevity. However, it is to be understood that such words are used in connection with the views in the drawings, and that, in actual use, the parts described by such words may have entirely different direction, relative position, and the like. Examples of such words are vertical, horizontal, upper, lower, etc.

In this application, the words fuse wire'are intended to describe and specify fuse wire that is on sale and is commercially known. Such fuse wire allows electric current to flow through such wire without blowing or melting the wire while the electric current is below a selected or specified ampere rating. Such fuse wire blows or melts when current above such selected or specified ampere rating flows through the wire. The sensitivity of the fuse wire, such as the length of time before blowing, may vary, depending on the various compositions, and other factors, of such well known fuse wires. In general, however, any well known fuse wire may be used in connection with this invention.

Referring now to FIGURES 1 and 2, an electric current sensitive fuse 10 may be constructed to blow while carrying electric current above a selected ampere rating, and not to blow while carrying electric current below such selected ampere rating. An electrically insulative rod 12 may be provided, which may be a substantially continuous cylinder or cylindraceous rod, if desired. Such rod 12 may have a straight or continuous longitudinal surface 16 along which a current carrying length of fuse wire, or fuse wire means 14 may extend along such surface 16 of the rod. Such rod 12 may be a solid rod, or it may be a hollow rod. The rod may be made of glass, or ceramic or plastic material, or any other suitable insulating material.

Two spaced, conductive current terminal fuse wire holders 18 may be secured over the ends of the rod 12, and they may be secured thereon by any suitable means, such as by press fitting. Such holders may be adhesively secured to the rod as by the use of epoxy adhesive cement, or the like.

The fuse wire 14 may be attached to the caps 18 in any suitable manner, as by spot Welding, swaging, or

soldering the fuse wire 14 to the outside of the fuse end' cap 18. Such welding, swaging, or soldering may be performed against the cap rim or bead 20, if desired, in a manner to cause the fuse wire 14 extensively to contact the surface 16 of the rod 12.

The construction is such that the fuse wire 14 extends along the surface 16, thereby damping any vibrations which may be produced in such fuse wire 14 by the passage of electric current, thus to prevent harmful effects from such vibrations.

The caps 18 have flange means extending along the side surface of the rod 12 to which the current carrying length of fuse wire 14 may be attached, such as to the rims 20 of such flange means, thereby materially to shorten the length and electrical resistance of such length of wire as compared to prior fuses of the same length of rod but having hollow rods with their length of fuse wire suspended from the centers of their end caps.

If desired, the construction of FIGURE 2 so far described may be encased in a casing 22, which may be a metallic casing, with an inward flange 24. This inward flange 24 extends into and is secured to the end disc 26 of the current carrying terminal 28, which carries current that is to be controlled by the fuse 10 of FIGURE 2. The casing 22 may be cylindrical and may be provided with an insulative sleeve 30. A compression spring 32 may be provided to engage the disc 26 at one end of the spring. The other end of the spring 32 may engage a silver plated contact ferrule 34, which surrounds the left end cap 18. The right end of the casing 22 is formed with a thinner casing portion 36, which surrounds a ceramic bushing 38. The bushing 38 engages the right end of insulative sleeve 30 and receives the current carrying terminal conductor 40 and its end disc or head 42. The terminal conductor 40 and head 42 may be inserted into the bushing 38, before the bushing is inserted in the thin portion 36 of the casing. Thereafter, the right end of the thinner casing portion 36 may be formed or bent into a flange 44 which secures and fastens the bushing 38 in the casing 22 and compressively holds all of the parts together inside such casing 22. Thereafter, an electrically insulative seal 46 may be formed around the end of the bushing 38, and around the terminal conductor 40, to seal the interior parts of the fuse construction within the casing 22.

In the embodiment of FIGURE 2, the current may be considered to flow, for example, from the terminal 28, through disc 26, spring 32, ferrule 34, left end cap 18, fuse wire 14, right end cap 18, disc or head 42, and right end terminal 40.

As long as the current flowing through this structure is below the selected ampere rating of the fuse, the fuse wire- 14 does not blow. Also the surface 16 of the rod 12 dampens any vibrations which might be caused in the fuse wire 14, and thus damage to such fuse wire by such vibrations is prevented. If the current passing from the terminal 28 to the terminal 40 should be above the selected ampere rating of the fuse 10, such fuse will blow by blowing the fuse wire 14 while such current is passing the length of fuse wire 14.

Harmful, continued vibrations of the wire 14 are not possible because of the extensive contact of such wire 14 along the surface 16 of the rod 12.

The phenomena of vibrating fuse wire is that it always attempts to oscillate in a somewhat rotary mode. By placing the fuse wire along the insulating rod, the oscillation is damped to the extent that the vibration problem is eliminated.

In the embodiment of FIGURE 3, the insulative rod 50 may be made of the same material as rod 12. However, the ends 52 of such rod 50 may be of reduced transverse dimension to receive the end caps 54 which may be silver plated copper or the like. All of the caps and the like herein disclosed may be made of silver plated copper, if desired. The outer diameter of the end caps 54 may be so constructed that the fuse wire 56 may be secured to the caps 54 by means of conductive epoxy cement, welding, staking or solder, in such a manner that the length of the fuse wire 56 between the caps 54 extends along the surface 58 of the rod 50. The conductive epoxy resin or cement may be any suitable conductive epoxy cement, such as is now on the market. Such conductive epoxy cement may be an epoxy cement which is filled with powdered conducting material, such as silver particles or silver plated copper particles. For example, the conductive epoxy cement known as Ecco Bond Solder No. 56C may be used, which is marketed by Emerson and Cuming, Inc. However, any other well known conductive epoxy cement may be used.

If desired, the structure shown in FIGURE 3 may be encased in a metal or plastic casing 60, which holds the two ceramic cups 62. These cups 62 receive the two spaced conductive current terminals 64, which have tapered discs or heads 66, which receive the inward flanges 68 of the end caps 54.

The casing 60 may, if desired, have a reduced diameter central portion 70, which may arrest the rims of the cups 62. Substantially airtight seals 72 may be placed and encased in the inwardly flanged portion 74 of the casing 60.

The action of the embodiment of FIGURE 3 is substantially the same as that of FIGURE 2 insofar as the action of the fuse wire means 56 is concerned. Such fuse wire means 56 extends along the surface 58 of the rod 50,.to dampen vibrations of the fuse wire 56, while it is carrying electric current below its ampere rating. This prevents harmful vibrations of the fuse wire during that time. The fuses of FIGURE 3, as well as of all other figures, blow when current above the ampere rating passes through them as elsewhere described.

The embodiment of FIGURE 5 may be substantially the same as that of FIGURE 3 except that the end caps 54A are received by the unreduced ends 52A of the rod 50A. The ends 52A are of the same transverse dimension or diameter as the main body of the tube or rod 50A. All of the other parts of FIGURE 5 are the same, as in FIGURE 3. They are therefore designated with only a few reference numerals which are the same as in FIG- URE 3 with the suffix A added. Therefore, they require no further description. In this embodiment of FIGURE 5, the fuse wire 56A is secured inside and between the end caps 54A and the rod ends 52A by means of conductive epoxy cement, or solder. The action of the length of fuse wire 56A in FIGURE 5 between the caps 54A is the same with respect to the outer surface 58A of the rod 50A as described in connection with corresponding parts in FIGURE 3.

In the embodiment of FIGURE 4, the rod may be hollow, so as to form a hollow cylindrical rod 80 with an interior surface 82, which may be a cylindrical interior surface. The fuse wire or fuse wire means 84 may be curled or pulled around the hollow ends 86 of the tube 80, so that the ends 88 of the wire are held by the resilient flanges 90 of the end caps 92. The end caps 92 may be secured to the end discs or heads 94 of the terminal conductors 96. The curled ends of the wire 84 may be secured between the flanges 90 and the ends 86 of the tube 80 with the use of conductive epoxy cement or solder 98. The conductive epoxy cement 98 may extend inwardly around the head 94 as shown at 100, and conductively to seal the interior of the tube 80 against the travel of air into and out of the tube.

In the embodiment of FIGURE 4. the length of fuse wire 84 is longer than the length of wire 14 or 56 of FIGURES 2, 3 and 5. The wire 84 is sufiiciently tight so that it is near the inner surface 82 of the tube 80, so that vibrations of the fuse wire are damped and cannot harmfully affect the length 84 of fuse wire. The wire 84 moves away from the rod surface 82 when heated by the electric current as shown in dotted lines at 84'.

In all of the embodiments, the disclosed rod can be made of glass, ceramic, plastic, or any other suitable insulating material. Oscillations or vibrations are dampened to the extent that the vibration problem is eliminated. This elimination of the damping problem is common to all embodiments of this invention.

FIGURES 6 and 7 show an embodiment in which a short insulative tube has a length of fuse wire means 112 secured to the ends 114 of such tube. Any type of construction may be provided to secure the fuse wire means ends 116 to the tube ends 114 so that a length of fuse wire means 112 is established to extend along the inner surface 118 of the tube 110 to conduct the electric current and have its vibrations damped substantially in the same manner as is done by lengths 14, 56 and 56A of fuse wire means in FIGURES 2, 3 and 5. This is accomplished by providing the length of tube 110 substantially of the same length as the active lengths 14, 56 and 56A of the fuse wire means of FIGURES 2, 3 and 5.

For example, the fuse wire means ends 116 may be curled or bent around the ends 114 of the tube 110. Then such fuse wire ends 116 are secured to the tube ends 114 in any suitable manner so that the fuse may be connected in the electric circuit to be controlled.

For example, a pair of spaced conductive current terminal fuse wire holders 120 may be secured to the wire ends 116. Such wire holders 120 may be conductive discs which are secured to the wire ends 116 and tube ends 114 with conductive epoxy cement 122.

If desired, the discs 120 may be provided with connectors 124 to connect the fuse in the electric circuit. Such discs 120 may be made of silverplated copper.

Other constructions may be used to secure the fuse wire means ends 116 to the tube ends 114, as desired.

Certain advantages are obtained from the short current carrying length of the fuse wire means 14, 56, 56A and 112. These fuse wire lengths are approximately onethird the length of the wire used in conventional fuses.

The significance of the shortened fuse wire lengths 14, 56, 56A and 112 is important in connection with low ampere or watt fuse rating. For example, for a given fuse rating, such as a one ampere fuse, using a given fuse wire material, a certain small diameter fuse wire is required. The diameter of this fuse'wire can be the same for any one of the fuses above discussed. Because of the small diameter of the fuse wire, at such low ampere rating, the electrical resistance of the fuse wire becomes a significant factor in particularly low voltage circuits. This resistance of the fuse wire causes adverse conditions, when it is a significant part of the total resistance of the electrical circuit being used, as is the case with long fuse wires. In some instances where it is necessary to use fuse wire whose resistance goes up significantly with the temperature, this problem becomes even more severe because of the fact that the resistance of the fuse wire can then rise to the extent that the current flow is restricted thereby resulting in a condition where the fuse wire does not reach a high enough temperature to melt and open the circuit. In other words, the fuse might then be acting as a current limiter. This is undesriable because the circuit is not then protected in the manner originally intended. With the shorter length of current carrying fuse wire in FIGURES 2, 3, 5 and 6, such short wire generally is not a significant part of the total resistance of the circuit being used, so that their short wire lengths can properly protect the circuit.

However, many of the advantages of this invention are also present in the embodiment of FIGURE 4, when used with a longer fuse wire. It is therefore to be seen that a new, unobvious and useful fuse construction has been provided.

In FIGURES 3 and 5, the reduced diameter central portion 70 of FIGURE 3 and the corresponding reduced diameter central portion of FIGURE 5 may be omitted. When these central portions are omitted the casings 60 and 60A may be uniformly cylindrical between the inwardly flanged portions 74 of FIGURE 3 and the corresponding inwardly flanged portions of FIGURE 5. Then the ceramic cups 62 of FIGURE 3 and the corresponding ceramic cups of FIGURE 5 may be :arrested by the tapered discs 66 of FIGURE 3 and corresponding discs of FIGURE 5 when the ceramic cups are inserted into the casings 60 and 60A before the inward flanges 74 are formed in FIGURE 3 and correspondingly in FIGURE 5.

FIGURE 1 shows how any of the fuses of this invention may be used in an electric current system. Such system may include different potential terminal means 130 and 132 to cause electric current to flow through said system. For example, the potential terminal means 130 may be any source of electric current supply, such as a battery, dynamo, transformer or the like, and may have its supply side connected to line 134, and may have its other side connected to ground 136 or the like. The line 134 may be connected to a switch 138 which may be connected to the fuse terminal 28, or any other fuse terminal herein disclosed. The other fuse terminal 40 may be connected to any electric current utilizing or electric current resistance means or load 140 which may also be connected to the electric line 142 which is connected to the other potential terminal means 132. The grounds are conductively connected, such as by ground, wire, or the like.

The fuse provides a minor electric resistance factor in the system, and the electric current utilizing or electric current resistance means 140 provides a major electric resistance factor in the system.

For example, in a system that normally operates at six volts, the fuse 10 may have a half or 0.5 ampere rating, and the electric current resistance means or load 140 may have 29 ohms resistance, thus providing substantially 30 ohms total resistance in the system. With the system operating under normal conditions, the electric current in the system would be 6-:30 or 0.2 ampere,

which is safely below the 0.5 ampere rating of the fuse. However, if a dead short should occur in the load 140, for example, the total resistance in the system would be reduced substantially to the 1 ohm of the fuse 10. This would cause an electric current to flow through the system which would be 6+1 or 6 amperes, which would be materially higher than the 0.5 ampere rating of the fuse 10 and would cause the fuse or fuse wire, to blow and break the circuit.

Thus, the fuse wires of the fuses of this invention may be any of the well known fuse wires having the desired ampere rating for the particular fuse to be made in accordance with this invention. Such fuse wires are available on the market and are supplied so that they have proper resistance and other characteristics so that they blow substantially at the deisred or specified ampere ratmg.

The illustrations in FIGURES 2-6 are all drawn in the application drawings at a 10:1 scale. That is, FIGURES 2-6 are ten times the actual size of a fuse according to this invention. However, it is to be understood that the fuses of this invention may be of different size from that indicated by these drawings.

While the form of the invention now preferred has been discolsed as required by statute, other forms may be used, all coming within the scope of the claimed subject matter which follows.

What is claimed is:

1. An electric current sensitive fuse constructed to blow while carrying electric current above a selected ampere rating comprising, an electrically insulative rod having a longitudinal surface, a current carrying length of generally straight fuse wire extending along and sulficiently near said longitudinal surface of said rod and being free to vibrate and be damped against harmful vibration by said longitudinal surface while said wire is carrying said electric current, and two spaced conductive current terminal fuse wire holders carried by said rod and connected to each end of said current carrying length of fuse wire to cause electric current passing through said current carrying length of fuse wire below said ampere rating to flow without blowing said fuse wire while causing said rod surface to damp vibrations in said current carrying length of fuse wire, and to cause electric current above said selected ampere rating to blow said current carrying length of fuse wire while passing through said current carrying length of fuse wire.

2. A fuse according to claim 1 in which said fuse wire holders are conductive caps secured at the ends of said rod.

3. A fuse according to claim 2 in which said conductive caps are cemented to the ends of said rod with conductive epoxy cement.

4. A fuse according to claim 1 in which said rod is cylindrical and has a substantially continuous longitudinal cylindrical surface damping said length of fuse wire while said length of fuse wire is carrying said electric current.

5. A fuse according to claim 4 in which said continuous longitudinal cylindrical surface is an outer surface of said rod.

6. A fuse according to claim -4 in which said rod is a hollow cylindrical rod, and said continuous longitudinal cylindrical surface is on the interior of said hollow cylindrical rod.

7. A fuse according to claim '6 in which said fuse wire holders are caps at the ends of said rod.

8. A fuse according to claim 6 in which said fuse wire holders are conductive members secured at hollow ends of said hollow rod.

9. A fuse according to claim '8 in which said fuse wire holders are conductive fiat members which close hollow ends of said hollow rod.

10. An electric current sensitive fuse according to claim 1 in which said fuse wire holders are connected in an electric current system including different potential terminal means for said system, a current resistance means connected in series with one of said ends of said current carrying length of fuse wire and with one of said potential terminal means, and wherein said resistance means provides a major electric resistance factor in said system, and said current carrying length of said fuse wire always carries substantially the entire current flowing through said current resistance means and provides a minor electric resistance factor in said system, the electric current of said system passing through said current carrying length of fuse wire without blowing said fuse wire while said electric current is below said ampere rating, and causing said fuse wire to blow when said electric current is appreciably above said ampere rating.

11. A fuse according to claim 1 in which said fuse wire holders are conductive caps with flange means extending along the surface of the rod, and in which said current carrying length of fuse wire is attached to said flange means to reduce said current carrying length of said fuse wire.

12. A fuse according to claim 11 in which said first named current carrying length of fuse wire is attached to the rims of said flange means of said caps.

References Cited UNITED STATES PATENTS HIRAM B. GILSON, Primary Examiner US. Cl. X.R. 337228, 231, 243 

